**Core Concept**
Diabetic nephropathy with frank proteinuria is a complication of diabetes mellitus characterized by damage to the renal glomeruli, leading to significant proteinuria. The management of hypertension in this scenario requires careful consideration of the underlying renal pathology to prevent further kidney damage.

**Why the Correct Answer is Right**
In patients with diabetic nephropathy and frank proteinuria, the goal of antihypertensive therapy is to reduce proteinuria and slow the progression of renal disease. Angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs) are the preferred initial therapy due to their ability to reduce proteinuria and protect the kidneys from further damage. This is achieved through their effect on the renin-angiotensin-aldosterone system (RAAS), which is activated in diabetic nephropathy.

**Why Each Wrong Option is Incorrect**
**Option A:** Other antihypertensive agents like calcium channel blockers or diuretics may not provide the same level of renal protection as ACEIs or ARBs in patients with diabetic nephropathy and proteinuria, making them less ideal choices.
**Option B:** Beta-blockers are not the preferred initial therapy for hypertension in patients with diabetic nephropathy and proteinuria, although they may be used as add-on therapy in certain cases.
**Option C:** Direct renin inhibitors are not the first-line treatment for hypertension in patients with diabetic nephropathy and proteinuria, due to their limited evidence of renal benefit and potential side effects.

**Clinical Pearl / High-Yield Fact**
In patients with diabetic nephropathy and proteinuria, the use of ACEIs or ARBs not only reduces blood pressure but also slows the progression of renal disease and reduces proteinuria.

**Correct Answer: C. Losartan, an ARB.**